The present disclosure relates to a reading device, as well as an image forming apparatus, and a reading device control method for conveying and reading a document.
A reading device (scanner) for reading a document to acquire image data may be provided in image forming apparatuses such as multifunction peripherals, copiers, printers and FAX devices. In another case, a type of reading device in which sheets of a set document are automatically and continuously conveyed to a reading position so as to allow a plurality of document sheets to be read in short time may be installed in image forming apparatuses. A known example of such document reading devices is as follows.
More specifically, in a conventionally known document reading device, a document fed from a document tray capable of accommodating a plurality of document sheets is introduced into the device, the introduced document sheet then being automatically conveyed. With a first document detection sensor placed near a downstream side of a sheet feed roller, and with a second document detection sensor placed near a downstream side of a conveyance roller placed on a downstream side of the sheet feed roller, a conveyance state of the document is detected based on detection signals outputted from the first document detection sensor and the second document detection sensor, respectively.
Some reading devices are designed to perform switchback of a conveyed document to read both sides of the document. Such a reading device saves the user the trouble of further setting a bottom side of a document subsequent to reading of its top surface. In the reading device with this system, a document that has been passed through a reading position to have one side read over is switched back, and then the switched-back document is fed back to the upstream side of the reading position so as to be passed again through the reading position to allow the other side of the document to be read.
In the switchback operation, a switchback roller pairs conveys the document, which has passed through the reading position (which has one side read over), once in such a direction as to once discharge the document out of the apparatus. Before the document is released from a nip of the switchback roller pair (before the document is discharged out), the switchback roller pair is rotated reverse. The switchback roller pair feeds the document onto a return conveyance path connected to the upstream side of the reading position. Front and rear of the document are reversed by this switchback operation.
When the switchback operation is executed before a rear end of the document passes through a branch point between a conveyance path ranging from the reading position to the switchback rollers and the return conveyance path, the document is fed back toward the direction in which the document has been conveyed. Such backward feed may cause a break or paper jam of the document. In some cases, timing for the switchback rollers to stop rotation and start reverse rotation is determined based on an output of a sensor provided on the conveyance path. Rotational stop and reverse rotation (switchback) of the switchback rollers are executed at a time point when it can be predicted that the rear end of the document has passed through the branch point from the sensor's detection of passage of the rear end of the document (i.e., a time point when a certain time has elapsed since the time point of detection of the passage of the rear end).
In this connection, there are some cases where a document having part of its rear end is cut off (i.e., cutout document) is set on the reading device. For example, a user may cut off part of the document by processing with scissors or a cutter. In a case where the cutout portion and a detection area of the sensor overlap with each other, the sensor detects a passage of a document rear end before a passage of a rearmost end (a tail end, non-cut-off portion) of the document through an installation position (installation line) of the sensor. In other words, the sensor detects a rear-end passage at a time point earlier than the time point that should be detected by the sensor. For this reason, the switchback may be started before the rearmost end of the document completely passes through the branch point. As a result, there may occur reverse feed, damage or paper jam of the cutout document. Accordingly, there is an issue that the switchback should be executed so as to prevent the cutout document from occurrence of damage or paper jam.
The known technique described above is other than relating to cutout documents. Therefore, the above-described known technique cannot cope with the problem involved in switchback operation of cutout documents. The known technique employs two sensors. In reading of a cutout document, there may occur a state misdetection when the cutout portion passes through a detection area of one sensor and non-cutout portion of the document passes through a detection area of the other sensor.